Recently, a Multiple Input Multiple Output (MIMO) technique for supporting a high information transmission rate is widely used in a mobile communication field. Not only a point-to-point MIMO technique but also multiple user MIMO techniques where a base station simultaneously considers a plurality of users who transmit data to a plurality of terminals, are being actively studied. Unlike a point-to-point MIMO, under a multiple user environment, information has to be simultaneously transmitted to a plurality of users in order to raise a transmission efficiency. More particularly, in the case where the number of transmission antennas is greater than the number of reception antennas, information has to be simultaneously transmitted to a plurality of users in order to obtain a maximum multiplexing efficiency. At this point, one of problems that may occur is that a signal of a certain user may act as an interference to a different user. The technique for canceling this interference signal may be classified into a transmission end interference cancel technique and a reception end interference cancel technique depending on a location of canceling the signal. When the number of transmission antennas is one, a method of decoding a signal of a different user and then canceling the signal at a reception end is best, and a transmission end interference cancel technique is not required. In contrast, when the number of transmission antennas is two or more, a method of canceling an interference at a reception end is not best and a transmission end interference cancel technique needs to be used. A Dirty Paper Coding (DPC), which is one of transmission end interference cancel techniques, supports a maximum information transmission rate. However, the DPC has a problem of having a considerably high calculation complexity.
Therefore, a Vector Perturbation (VP) technique having a lower calculation complexity than that of the DPC has been suggested. The VP technique is a linear pre-processing technique based on zero-forcing. In the VP technique, a transmission end adds an integer perturbation vector to a desired signal vector in order to prevent a power boosting phenomenon.
As described above, the VP technique may obtain a performance gain compared to an existing linear technique by adding an integer perturbation vector before sending a signal via a transmission antenna, but requires a high calculation complexity during a process of finding out an optimum integer perturbation vector whenever a channel response and a data signal change.
Therefore, an apparatus and a method for determining an optimum integer perturbation vector requiring a low complexity in a multiple antenna system are required.